Different experience here, I and another sibling had the same initials as a parent i.e. Two S Smiths, and two D Smiths in the household. As late teens and adults, even with different second initials, it has caused beaurocracy fuck ups where computers or staff in a hurry decided there were obviously only two people not four, or it was one person who had moved house rather than two people at two different addresses (AA and British Gas I'm looking at you) and merged accounts. It still happens often enough and has caused enough minor issues that we're careful about not using the same banks.